"Whoever believes that Jesus is the Christ is born of God, and whoever loves the Father loves the child born of Him. By this we know that we love the children of God, when we love God and observe His commandments."
1 John 5:1
How do we know we are "born of God"? That we are saved? This is evidence of salvation: to believe that Jesus Christ is the Son of God. The one who believes -- who has staked their eternal life on this truth -- has died to the "old self" and has been born again. A spiritual rebirth. It is not our belief that saves us. It is only by God's grace that we are saved. We are transformed by Him when we place our faith in Jesus. Further evidence is that we love other Christians, and by loving other Christians we show that we love God, since we are obedient to His command to love others.
". . . the risk of a counterfeit Christianity is so strong. There are people who are naturally compassionate (just like those who are naturally sour). It is part of their personality. There are those who are naturally rule-keepers (just like there are natural rebels). Still others are naturally academic and quick to believe (just as there are others who seem to be natural skeptics). We are not saved by our personality! We are saved by the work of God inside of us. The evidence that we are a child of God is that we see ALL THREE of these things in our lives:
A belief and surrender to Jesus as God become man who is our way of salvation
Increasing love for God and for others
Obedience to God’s commands" (Bruce Goettsche)